1. Field of the Invention
The present invention relates to a radiation imaging system for radiographing a radiation image of an object and a driving method thereof.
2. Description of the Related Art
In general, a demand for digitalization of an x-ray image in the hospital has been recently increasing. In reality, a radiation imaging apparatus such as, for example, FPD (Flat Panel Detector) has began to be used, in which an x-ray dosage is converted into electric signals by using a solid state imaging device in which x-ray detection elements (conversion elements) are disposed in a two-dimensional array pattern instead of a film.
In this X-ray imaging apparatus, since an X-ray image can be replaced by digital information, the image information can be transferred far away and instantaneously and this provides the advantage of being able to receive a sophisticated diagnosis comparable to a university hospital in the heart of the city, while being far away. Further, there is also the advantage of being able to save a storing space of the film in the hospital in case the film is not used. In future, if an excellent image processing technology can be introduced, an automatic diagnosis using a computer without an intermediary of a radiologist can be expected with great hopes.
In recent years, a radiation imaging apparatus has been put to practical use, in which an amorphous silicon thin film semiconductor is used for the solid state imaging device so as to radiograph a static image. Specifically, by using the manufacturing technology of the amorphous silicon thin film semiconductor, the radiation imaging apparatus comprising a solid state imaging device enlarged in its area exceeding 40 cm square to cover the size of human chest regions has been realized. This radiation imaging apparatus, because of relative easiness of its manufacturing process, is expected to provide an inexpensive apparatus in future. Moreover, since the amorphous silicon can be manufactured on a thin glass plate below 1 mm, it has an advantage of being able to make the thickness extremely thin as a detector. Such a radiation imaging apparatus, for example, is disclosed in Japanese Patent Application Laid-Open No. H08-116044.
Further, more recently, development of radiographing a moving image is underway in such a radiation imaging apparatus. If such a radiation imaging apparatus can be manufactured at a moderate price, the still image and moving image can be radiographed by the same one set, so that popularization of the apparatus can be expected in many hospitals.